| Summary: | peer reviewed Rivers fragmentation and homogenization to enable man-made activities, such as navigation, hydropower production and water regulation, caused a drastic reduction and the extinction of several migratory fish species. Mitigation of this key issue affecting biodiversity while preserving benefits of rivers exploitation requires a detailed understanding of the migratory fish behavior depending on hydrodynamic conditions. This study considers the case of the Meuse river in Belgium close to Monsin dam. At this location, the junction of the Ourthe river, a large tributary of the Meuse, the main river division in two branches and the intake of the Albert Canal, create specific flow conditions and offer several routes prone to significantly affect downstream migrating fish. Data from acoustic tagged Atlantic Salmon smolts (n=91) collected in the framework of the EU funded Life project Life4Fish are analyzed to explain how discharge evolution along time, water level control by the dam and discharge partition between the Canal and the main river affect migration route selected by the fish and the time needed to make this choice. The results show that the main factor affecting success of smolts migration is the flow velocity. This velocity is strongly affected by the dam regulation, making the Albert Canal, an unsafe migration route, more or less attractive than the Meuse river depending on discharge evolution. 14. Life below water 7. Affordable and clean energy 13. Climate action
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